Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> writes:
Hi Alexey,
On 1/4/22 12:51, Alexey Gladkov wrote:They are not.
Right now, the mqueue sysctls take ipc namespaces into account in aCould you crosscheck that all (relevant) allocations in ipc/mqueue.c
rather hacky way. This works in most cases, but does not respect the
user namespace.
Within the user namespace, the user cannot change the /proc/sys/fs/mqueue/*
parametres. This poses a problem in the rootless containers.
To solve this I changed the implementation of the mqueue sysctls just
like some other sysctls.
Before this change:
$ echo 5 | unshare -r -U -i tee /proc/sys/fs/mqueue/msg_max
tee: /proc/sys/fs/mqueue/msg_max: Permission denied
5
use GFP_KERNEL_ACCOUNT?
We should not allow normal users to use up all memory.Saying the cgroup kernel memory limit is the only thing that works, and
Otherwise:
The idea is good, the limits do not really prevent using up all
memory, _ACCOUNT is the better approach.
And with _ACCOUNT, it doesn't hurt that the namespace root is able to
set limits.
that is always better is silly.
First the cgroup kernel memory limits noted with ACCOUNT are not
acceptable on several kernel hot paths because they are so expensive.
Further the memory cgroup kernel memory limit is not always delegated to
non-root users, which precludes using the memory cgroup kernel memory
limit in many situations.
The RLIMIT_MQUEUE limit definitely works, and as I read the kernel
source correct it defaults to MQ_BYTES_MAX aka 819200. A limit of
800KiB should prevent using up all of system memory, except on very low
memory machines.
So please let's not confuse apples and oranges, and let's use the toolsI'll try to check the patch in detail in the next few days.
in the kernel where they work, and not set them up in contest with each
other.
Rlimits with generous but real limits in general are good at catching
when a program misbehaves. The cgroups are better at setting a total
memory cap. In this case the rlimit cap is low enough it simply should
not matter.
What has been fixed with the ucount rlimits is that (baring
implementation bugs) it is now not possible to create a user namespace
and escape your rlimits by using multiple users.